1. Field of the Invention
The present invention relates to a vacuum transfer system of a semiconductor device fabrication facility. More particularly, the present invention relates to a device of the system through which a vacuum is introduced to a vacuum chuck for evacuating the chuck to cause a wafer to adhere thereto.
2. Description of the Related Art
Generally, the fabrication of semiconductor devices is a sensitive process requiring strictly controlled processing conditions, and precise manufacturing techniques. The semiconductor device fabrication facility includes a vacuum transfer system through which the force of a vacuum, created by a vacuum pump, is transferred to a vacuum chuck to secure by suction a wafer to the chuck.
A conventional vacuum transfer system will now be described referring to FIGS. 1 and 2. The conventional vacuum transfer system 10 comprises a lower plate 20 having a vacuum port 16, a thermocouple 18 protruding from the front of the lower plate 20 adjacent the vacuum port 16, an upper plate 12 fixed in place in the device, and a pushing unit 24 fixed to the upper plate 12 for moving the lower plate 20 toward a vacuum chuck 22.
The lower plate 20 is coupled to the upper plate 12 by a guide 14 fixed to the lower plate 20. A guide rail (not shown) is provided on the bottom of the upper plate 12. The guide rail is connected to the guide 14, and the lower plate 20 is moved back and forth along the guide rail.
The vacuum port 16 faces the vacuum chuck 22. The thermocouple 18 terminates adjacent the end of the vacuum port 16 in order to detect the temperature at the location at which a wafer is mounted to the vacuum chuck 22.
In addition, the lower plate 20 has a recess 28 in one side thereof. The recess is defined by an inclined surface 26 which extends at an angle relative to the longitudinal direction of the guide rail. The width of the lower plate 20 is thus reduced at the recess 28.
The pushing unit 24 includes a plate spring 30 which is folded over on itself. When the ends of the plate spring 30 are moved away from each other, the elasticity of the plate spring 30 gives rise to a restoring force which urges both ends back toward each other. There is a rectangular locking slot 32 in one end of the plate spring 30. The plate spring 30 is fixed on the side of the upper plate 12 by two locking bolts 34 which pass through the locking slot 32. The position of the plate spring 30 can be adjusted by loosening the locking bolts 34, moving the plate spring 30 to a desired position as allowed for by the locking slot 34, and then tightening the locking bolts 34. In addition, the pushing unit 24 includes a vertically extending roller pin 36 fixed to the other end of the plate spring 30, and a roller 38 rotatably supported by the roller pin 36 and urged by the plate spring 30 against the inclined surface 26.
The lower plate 20 is driven to the vacuum chuck 22 by the pushing unit 24 to move the end of the vacuum port 16 into contact with the vacuum chuck 22 whereupon air in the chuck 22 is evacuated through the vacuum port 16.
More specifically, an operator moves the lower plate 20 toward the vacuum chuck 22 until the roller 38 comes into contact with the inclined surface 26. Then, as the roller 38 applies pressure to the inclined surface 26 under the restoring force exerted by the plate spring 30, the lower plate 20 is slid toward the vacuum chuck 22 as guided by the guide rail. The roller 38 continues to move along the inclined surface 26 until the end of the vacuum port 16 contacts the vacuum chuck 22 and the roller 38 comes to rest at a certain location on surface 26.
Typically, the elasticity of the plate spring 30 causes an excessive force to be applied between the contact of the end of the vacuum port 16 and the vacuum chuck 22. Thus, these members can be damaged due to the excessive shock. In an attempt to mitigate this problem, the locking bolts 34 are loosened, and the plate spring 30 is repositioned toward the rear of the upper plate 12 so that less force is exerted on the lower plate 20 when the vacuum port 16 meets the vacuum chuck 22.
On the other hand, the plate spring 30 becomes less resilient over time due to its continuously being deformed while in use, and due to its handling while it is being mounted to and disassembled from the upper plate 12. In this case, the locking bolts 34 are loosened, and the plate spring 30 is repositioned toward the front of the upper plate 12 so that more force will be exerted on the lower plate 20 by the plate spring 30 when the vacuum port 16 meets the vacuum chuck 22.
However, as the plate spring 30 continues to lose its elasticity, eventually a gap will be formed between the vacuum chuck 22 and the vacuum port 16. In this case, a vacuum will not be produced in the vacuum chuck 22 via the vacuum port 16, and the plate spring 30 thus cannot be used any more. Accordingly, the plate spring 30 must be replaced with another plate spring having the same size and elasticity. Such replacement costs add to the cost of manufacturing the semiconductor devices.
In addition, when replacing the plate spring, it is difficult to locate the spring at the precise position which will cause the vacuum port 16 to meet the vacuum chuck 22 without a gap being left therebetween or without excessive shock being generated therebetween. Furthermore, the time and effort it takes to replace the plate spring and correctly position the new plate spring compromises the operation efficiency of the facility.